Datasheet

10-2
Cisco ONS 15454 SDH Reference Manual, R7.0
October 2008
Chapter 10 Timing
10.2 Network Timing
card. However, if you assign all three references to other timing sources, the internal clock is always
available as a backup timing reference. The internal clock is a Stratum 3 (ST3), so if an ONS 15454 SDH
node becomes isolated, timing is maintained at the ST3 level.
The CTC Maintenance > Timing > Report tabs show current timing information for an ONS 15454 SDH,
including the timing mode, clock state and status, switch type, and reference data.
Caution Mixed timing allows you to select both external and line timing sources. However, Cisco does not
recommend its use because it can create timing loops. Use this mode with caution.
Note Only one port can be used for timing related provisioning per line card on the Cisco ONS 15454 SDH
platform.
10.2 Network Timing
Figure 10-1 shows an ONS 15454 SDH network timing setup example. Node 1 is set to external timing.
Two timing references are set to BITS. These are Stratum 1 timing sources wired to the BITS MIC-C/T/P
coaxial connectors on Node 1. The third reference is set to internal clock. The BITS outputs on Node 3
provide timing to outside equipment, such as a digital access line access multiplexer.
In the example, Slots 5 and 6 contain the trunk (span) cards. Timing at Nodes 2, 3, and 4 is set to line,
and the timing references are set to the trunk cards based on distance from the BITS source. Reference 1
is set to the trunk card closest to the BITS source. At Node 2, Reference 1 is Slot 5 because it is
connected to Node 1. At Node 4, Reference 1 is set to Slot 6 because it is connected to Node 1. At
Node 3, Reference 1 could be either trunk card because they are an equal distance from Node 1.